1. Field of the Invention
The present invention relates to a solar radiation heat influx sensor for an automotive vehicle which can accurately detect solar radiation heat influx due to rays of sunlight falling on the vehicle body in order to adjust an air-conditioning system for controlling passenger compartment air temperature.
2. Description of the Prior Art
Conventionally, there exist solar radiation heat influx sensors for an automotive vehicles such that a first temperature, T.sub.1, at a position within a passenger compartment where solar radiation is directly applied, and a second temperature, T.sub.2, at another position within the passenger compartment where no solar radiation is directly applied, are detected separately. The solar radiation heat influx is obtained by multiplying the difference in temperature between T.sub.1 and T.sub.2 by a predetermined correction factor. See, for example Japan, Published unexamined patent application No. S55-72410.
In the above-mentioned prior-art solar radiation heat influx sensor, the sensor detecting the temperature T.sub.1 is disposed at a position subject to insolation, for instance, on the top of an instrument panel or on a rear parcel shelf; the sensor detecting the temperature T.sub.2 is disposed at a position not subject to insolation, for instance, under the instrument panel.
In general, when a vehicle is travelling, however, the position subject to solar energy within a passenger compartment varies according to the direction in which the vehicle is travelling or according to the time at which the vehicle is travelling. For example, even if a solar radiation heat influx sensor is disposed on top of an instrument panel so as to receive solar energy through the front windshield glass, it will cool to normal passenger compartment temperature when the vehicle is not travelling toward the sun. It is practically impossible for a single sensor to receive solar energy at all times and, therefore, impossible to accurately detect solar radiation heat influx by this method.
Further, the flow of air within the passenger compartment varies according to the operating conditions of the air-conditioning system. When the flow of air varies, the correction factor, multiplied by the difference in temperature between T.sub.1 and T.sub.2 to obtain solar radiation heat influx, also varies. Since the correction factor for the above-mentioned sensor must be predetermined under average conditions, it is impossible to accurately detect solar radiation heat influx as conditions change.